I had an "Sheets(1).Activate" right before the loop started, but when the
code started failing in the middle of the workbook, we commented that out,
so that we could start at the currently selected sheet.

Yes, an Error 91 does pop-out when they get to the end of the workbook,
which is why I handled it in the EH. The thing is, that this particular
error occurs in the middle of the workbook. <shrug> I first thought it was
something wrong with the particular sheet, however, you can restart the
macro on the sheet previous, and the code will run as expected until it gets
to the end of the workbook. <sigh> Nothing for me to be able to say "Ah HA"
about.